P2 assistant software problem on Mac

I am trying to download and install the P2 assistant v.3.8 and the RC assistant on my Mac with OS X 7.5. They seem to download fine, but when I try to open them by clicking on the PT2 icon, I get a message that the installer suddenly closed. I followed the istructions from the new manual v.1.4. Any thoughts on what I may be doing wrong?